Process for the separation and recovery of inorganic salts



fiatented Feta. 7,

UNITED STATES ()FFICE 2,496,288' raooiiss roars); SEPARATION AND ascovsux or INoaGANio SALTS Clifford a. Hamper, Harvey, I 'l1., assiggii ortil Cardox Corporation, Chicago, 111., a. corpora"- tion of Illinois No Drawing. Apiilicatiorrflitiarch 20,1945, Sriai N0. 736,113

The insoluble calcium su1fate is separated from the mixture by filtration leaving a solution containing equivalent amounts of sodium c'hlorite and potassium chlorate. Mixtures of sodium chlorite and potassium chlorate may be other- Wise produced and the present invention is primarily concerned with and has as its object the provision of a process for expeditiously separating sodium chlorite and potassium chlorate from mixtures thereof, irrespective of themanner in which such mixtures are produced.

It has been ascertained that the amount of water required to keep theequi-mole mixture of sodium chlorit'e and potassium chlorate in solua tion will varyironi about 38 moles of water per moleof sodium chlorite plus mole of potassium chlorate (1 mole oftotal salts) at 25 C., to about 15.5 moles of water at 60 C. As thetemperature is lowered the amount of water required is greater and, of course, as the temperature increases the amount of water required to keep the equi-mole mixture of these salts in solution is less. It is to be borne in mind that the mole ratio of sodium chlorite to; potassium. chlorate neednot always be 1 tom 1. The ratio may be higher or lower and-jstill permit of separation of the two salts in accordance with the process of the present invention.

When water is removed, at temperatures above 34 (3., from a solution containing sodium chlorite andpotassium chlorate amounts upto' about 92 mole percent sodium chlorite and 8 mom percent potassium chlorate, only the potassium ch10.- rate will be precipitated after the solution be comes saturated. So long as the mole ratio of 92 sodium chlorite to 8 potassium chlorate is not exceeded, due to the precipitation of potassium chlorate from the solution, no sodium chlorite will; be precipitated.

maccordance with the present invention; a

solution containing both sodium chlorite and potassium chlorate. is subjected to progressive evaj'obratioh at temiieraturesabove 34 C., but below the temperature at which the decompositij'on of s'cdiiim chlorite comes appreciable, and the estate of eva oratib oiitroued so that the mole ratio of 92 sodium chlorite to 8 potassium chlorate is not ex'cfded' to thereby precipitate hotass'ium chlorate from the solution which is removed by filtration orcentriiuging.

The water are be r ring the progressive evaporation redpressureconditioiis, i. 1'1" ,sub atmos oheric Inasmuch as were emu e elevated ternioer at1ire,

@ iii. The decomp sition terrigerature of sodium hiorite variessomewhat with the pH of the solution as well as with the presence of other compounds. Prolonged l e tiiig or the sodium chlorite" containing soliitibffis'hould" alsofbe avoided. However, it has steamed tl fat'it is possible to adequately concentrate a sodium chlorite con taming solution at, atmospheric oressure without substantial deleterious dcohrpositioi'i 0f the cl'i'lorite. we I M Inasmuch as solidfiiotassium chlorate is formed upon removaloi waiter from the solution, the lat-- ter becomesmorecoficentrated withrespect tosodium chlorite use less concentrated with respect to potassium chlorate a's'the rirogressi ve evapora tion proceeds. This action causes the mole ratio of sodium chiori te to ews-sum chlorate in t e Somme to. orogr" my" increase. When the mole ratioiri' thejso es'aboutQZ sodium emorite to: 3 eotas'si chlor'ate', progr ssive evaporation is top ridthefcroh'or solid pfitas sium chlorate rem d"by filtration oi by cen trifug'ing. W H The mole ratio" of; about sz' 'dium chlorit'e to 8potassiumi Grimmer esfents'ftl'i iccom position of solutions stem ra u'res up toabout3l? CL Theamountdf waterassoc'iated with any giveh duar'iti'ti of sodiui'ii chlorite and potassium lorate th'aliov ucu a eutectic solution will vary with. the temperature; The higher the te perate tliles's is" the amo nt of water requi e to] e-p" a? givif'amount or 92sodiuni ch r'ite"to"8pota's'siiim chlorateiriix turelin solution. H

W'hen water isfrci ioved r mtteeuteeucfniixture at itssaturat nterii e;. aso1id'miX- sium chlorate will be precipitated in exactly the same ratio as they exist in the solution. Furthermore, as a eutectic solution of sodium chlorite and potassium chlorate is cooled below its satura tion temperature, i. e., temperatures below 34 C. there will be precipitated a solid mixture of sodium chlorite and potassium chlorate of the same ratio of these solids as prevails in the solution.

It follows that when a solution of sodium ch10- rite and potassium chlorate whose mole ratio content is less than 92 sodium chlorite to 8 potassium chlorate is evaporated to the eutectic ratio of sodium chlorite to potassium chlorate, the same quantity of potassium chlorate will be deposited as a solid no matter whether sufllcient water is removed to equal C. eutectic composition or the 34 C. eutectic composition. The respective eutectic solution compositions at temperatures up to 34 C. depend upon a corresponding water content. If water is removed from the C. eutectic solution, for example, the temperature must be maintained at a higher point to keep both of the salts in solution. This relationship, however, holds only up to about 34 C. for this particular system. At temperatures above 34 C.

the eutectic solution compositions will no longer remain at the mole ratio of 92 sodium chlorite to 8 potassium chlorate. At these higher temperatures the solutions become less rich in sodium chlorite.

When the progressive evaporation, accompanied by separation of potassium chlorate, has proceeded to a point where the mole ratio of sodium chlorite to potassium chlorate is approximately 92 sodium chlorite to 8 potassium chlorate, the remaining solution or filtrate can be further treated for the recovery of sodium chlorite. Alternative procedures may be followed from this point forward in the recovery of sodium chlorite and, if desired, some additional potassium chlorate.

One of the alternative procedures for treating this solution, following the progressive evaporation and at a time when the mole ratio of sodium chlorite to potassium chlorate in the solution is of the order. of 92 sodium chlorite to 8 potassium chlorate, is as follows. The solution is at a temperature well above 34 C. and approximately 60 C. and, therefore, well above the transition temperature of sodium chlorite so that the solution at this point contains no NaClO2'3I-I2O crystals. By cooling the solution to a temperature of about 25 C., and in the absence of NaC1O2-3H2O crystals, 2, further crop of potassium chlorate can be precipitated and separated from the solution. The remaining solution may then be seeded with a few NaClO2-3H2O crystals and a ver substantial amount of sodium chlorite precipitated as NaClOz-3H2O. The mother liquor from the latter step is advantageously recycled to the initial progressive evaporation step. Where anhydrous chlorite is desired, the precipitated and separated NaC1O2'3I-I2O ma be heated to a temperature above 38 C., the transition temperature thereof, to insure against the presence of NaClOz-3H2O crystals and the thus heated solution cooled down to a temperature of 25 C. in the absence of NaC1O2-3H2O crystals, under which conditions a substantial amount of anhydrous sodium chlorite can be precipitated and separated out. Indeed, it has been discovered that a super-saturated solution of NaClOz which has been heated above the transition temperature to insure against the presence of NaClOz-3H2O crystals can be cooled to a temperature of the order of 25 C. without reconversion of NaClOz-3H2O crystals to efiect precipitation of anhydrous sodium chlorite.

In the foregoing outlined procedure, if desired, the mother liquor, following the precipitation and separation of NaClOz-3H2O, instead of being directly recycled to the progressive evaporation step, may be evaporated separately at a temperature of the order of 60 C. and filtered hot to precipitate out additional anhydrous sodium chlorite, the resulting filtrate being then recycled to the initial progressive evaporation step.

An alternative procedure for recovery of sodium chlorite and, if desired, some additional potassium chlorate from the solution leaving the progressive evaporation step of the process, which solution, as has been noted, has a mole ratio of sodium chlorite to potassium chlorate of about 92 sodium chlorite to 8 potassium chlorate, is as follows: The solution leaving the progressive evaporation step ma be further concentrated by driving ofi some additional waler at a temperature of the order of 60 C. and then filtered at this temperature to separate out anhydrous sodium chlorite. The filtrate, following the separation of anhydrous sodium chlorite, may be directly recycled to the progressive evaporation step of the process or, if desired, this filtrate may be cooled to a temperature of approximately 34 C. to precipitate some additional potassium chlorate, which is filtered out at this temperature, and the remaining filtrate then recycled to the progressive evaporation step of the process.

Still a further alternative procedure for treating the solution leaving the progressive evaporation step of the process and which solution, as

I stated, has a mole ratio of sodium chlorite to potassium chlorate of about 92 sodium chlorite to 8 potassium chlorate, is as follows: The solution may be progressively cooled down to a temperature of the order of 15 C., at which temperature there will be precipitated a mixture of potassium chlorate and NaC1O2'3H2O in the same ratio as these compounds occupy in the solution. The mixture may be separated out by filtration and then heated to a temperature of the order of 45 C., at which temperature anhydrous sodium chlorite may be filtered out and the filtrate recycled to the initial progressive evaporation step of the process.

The following constitute examples of the various procedures which may be carried out pursuant to the present invention.

Example 1 Fifteen hundred and sixty-three parts of a solution composed of 5.75% NaClOz, 7.85% K0103 and 86.4% H2O were progressively evaporated stepwise at over 34 C., the K0103 precipitated being filtered off at intervals as the evaporation went on. After a total of 1,271 parts of water had been evaporated, the solution composition at 34 C. was 50% NaClOz, 5.5% KClOs and 44.5% H2O. The total KClOs recovered as a solid at temperatures of 34 C. or over amounted to 111 parts.

The filtrate at 34 C. was again evaporated at a temperature over 60 C.'until 40.4 parts of water had been removed. By filtering the resultant slurry at 60 C., 45 parts of solid anhydrous NaClOa were separated leaving a solution whose composition was 47.2% NaClOz.

acemes-s 10.8% K0102. and 42% E20. After the Na0l0z crop had been obtained the filtrate was added to another batch of the starting solution and the mixture was put thru a second cycle similar to the one described.

In an alternative operation, the filtrate was cooled to 34 0. and a second crop of 5.3 parts of K0103 separated. The mother liquor from this 34 0. filtration was added to another batch.

each cycle.

Example 2 To 151.2 parts of the mother liquor from-a previous cycle was added a solution having a 1:1 mole Na0l02, 122.6 parts K0103 and 1,350 parts H20. The combined solution was progressively evaporated with separation at several points of the solid K0103 formed during the water removal until the solution composition reached 47.2% NaClOz, 10.8% X0103 and 42.0% H at 60 C. 'The solution was then cooled in the absence of anysolid sodium chloritetrihydrate to 0. and more K0103 was filtered off as a solid. The total K0103 separated as 'a -solid during the evaporation and this cooling amounted to 122.6 parts.

ratio NaClOatKClOs and containing 90.5 parts --After all of the solid K0103 had been removedthe *filtratewas seeded with a fewcrystalsof Na0l02'3l- I2 0 When the temperature had again reached 25C.,

"a crop of 144.5 parts-of Na0l0z-3Hz0 was recovered by filtration. This sodium chlorite crystal crop contained the equivalentof 90.5parts of anhydrous NaClOz. The mother liquor, composed of 63.2 parts NaClOz, 7.4 parts K0103 and 80.6 parts of H20, was recycled from this operation along with the next batch.

To obtain anhydrous N a0lOz the NaC1O2'3H2O crystals were heated aboveabout 38 0., the transition temperature in the absence of other salts,

to form a slurry of solid anhydrous NaClOz in a saturated sodium chlorite solution. After the crystals were melted'they were cooled to a temperature below the transition temperature, in'the absence of NaClOz-BHzO, and the "solid Na0lO2 separated by filtration.

Example 3 The mother liquor from Example 2, consisting of a solution, at 25 0., of 63.2 parts of'NaClOz, 7 .4 parts of K0103 and 80.6 parts of H20 was evaporated until the mixture contained 64.3% NaClOa, 7.2% K0103 and 28.5% H20. The water removed was 52.9 parts. This mixture was a slurry containing solid Na0l02, and by filtering at 60 0., a crop of 31.6 parts of solid anhydrous Na0l02 was recovered,leaving as a filtrate 66.? parts of a solution of composition 47.2% NaClOz, 10.8% K0103 and 42.0% H20. This final filtrate was recycled with the next batch being treated.

Ewample 4 K0103 and 44.5% H20. During the evaporation of the 1269.2 parts "of water needed to reach this point, a total of 122.6 parts of solid K0103 formed and was separated by filtration at several intervals. After the final K0103 removal, the remaining 349 parts of mother liquor was cooled stepwise to 15 0. to cause the precipitation of a solid mixture totaling 14.3 parts of K0l03 and 201.2 parts of NaC1O23I-I2O which was filtered oil at 15 0.

The 133.5 parts of filtrate were recycled with the next batch. The above solid mixture was heated to dissolve all of the K0103, the

NaClOz 31-120 being decomposed to NaClOz and E20 by the heating. Sodium chlorite in the amount of 39.0

.parts remained as a solid and was recovered by filtration at this temperature of about 45 0. The mother liquor was added to the next batch.

Certain operations for the manufacture of sodium chlorite and potassium chlorate will yield solid mixtures of coprecipitated Na0l0z-3Hz0 and K0103. Such mixtures can be separated by following the treatment outlined in the latter part of Example 4 above, consisting of heating the mixture above the NaClOz-BHzO transition temperature to such a temperature that all of the K0103 is dissolved in the water associated with the Na0102-3l-I20. While most of the water will come from the water of crystallization of the sodium chlorite trihydrate, some will be derived from the mother liquor adhering to such a solid mixture after the filtration or washing.

Assuming, however, that all of the water which will be present uponheating such a mixture above 34 0. comes from the trihydrate, the maximum K0103 content of mixtures amenable to this separation method will be between 20 and 25% K0103 on a dry basis. Such a mixture may be heated to near the boiling point of the resultant slurry to dissolve all of the K0103 contained therein.

Solid mixtures of NaClOz and K0103 containing more than 20-25% KClOs on the dr basis may be separated byadding suificient water to bring all of the NaClOz into solution at some temperature above about 3 l 0., then cooling to some temperature below this initial one but not ,mixtureof sodium chlorite and potassium chlorate, either solid or in solution, may be treated forthe separate recovery of both salts. It may be pointed out that any solution containing Na0l02 and K0103 in ratios less than about NaClOz to 10% K0103 by weight and H20 in the ratio of'at least about 47% H20 to -53 Na0l0z by weight at anytemperature will precipitate K0103 only when cooled to a lower temperature.

In any case the precipitation of one salt only can proceed only until the solution remaining contains NaClOz and K0103 in a weight ratio of about 9 to 1. Cooling of any solution of this -Na0l0z to K0103 ratio will cause the two salts to be deposited as a mixture of this ratio. The

weight ratio of 90 NaClOz to 10 K0103 corresponds to a mole ratio of 92 to 8.

Reference is made to the following copending applications which are related to the invention amass herein disclosed; application S. N. 647,396,- now Patent No. 2,489,571, which discloses a process for the preparation of perchlorates and chlorites of different metals; application S. N. 647,403, now Patent No. 2,489,572, which relates to a process for the preparation of chlorine dioxide and a metal perchlorate; application S. N. 647,404, now Patent No. 2,489,573, which relates to a process for the preparation of chlorates and chlorites of different metals; and application S. N. 756,542 which relates to a process for the resolution of mixtures of sodium chlorate and sodiumchlorite.

Having thus described my invention, what I claim is:

1. A process for the separation of sodium chlorite and potassium chlorate from solutions containing these salts which comprises progressively evaporating the solution at temperatures above 34 C. so as to crystallize potassium chlorate until the solution reaches the eutectic composition having a saturation temperature of about 34 C., separating the thus crystallized potassium chlorate, thereafter cooling the remaining solution below 34 C. to crystallize a mixture of potassium chlorate and NaClOz-SHzO, separating the mixture from the mother liquor, heating the mixture above the transition point of NaClO2-3H2O to dissolve the potassium chlorate and to form a slurry of solid anhydrous sodium chlorite in a saturated solution thereof, and separating the solid sodium chlorite from the heated solution.

2. A process for the separation of sodium chlorite and potassium chlorate from solutions containing these salts which comprises progressively evaporating the solution at a temperature above 34 C. to crystallize potassium chlorate until solution approximates the eutectic composition having a saturation temperature of about 34 C., separating the potassium chlorate thus crystallized, thereafter recovering sodium chlo-' rite from the remaining solution by evaporating said remaining solution at a temperature higher than that of the initial evaporation until the solution is saturated with respect to the residual potassium chlorate so as to crystallize anhydrous sodium chlorite, separating the thus crystallized anhydrous sodium chlorite from the mother liquor at such higher temperature, and thereafter cooling the mother liquor to 34 C. so as to crystallize therefrom additional amounts of potassium chlorate.

3. A process for the separation of sodium chlorite and potassium chlorate from solutions containing these salts which comprises progressively evaporating the solution at a temperature above 34 C. to crystallize potassium chlorate until solution approximates the eutectic composition having a saturation temperature of about 34 C., separating the potassium chlorate thus crystallized, and thereafter cooling the remaining solu tion in the absence of solid NaC1Oz-3H2O to about 25 C. and separating therefrom at said lower temperature an additional amount of crystallized potassium chlorate, thereafter seeding the remaining solution with NaClOz-3Hz0 crystals to crystallize NaClO2'3l-I2O, and separating the thus crystallized N aClO2'3E-IzO from the mother liquor.

4. A process according to claim 3 in which the mother liquor is subjected to further concentration at a temperature higher than that of the initial evaporation until the solution is saturated with respect to potassium chlorate so as to crystallize' anhydrous sodium chlorite only, and separating the thus crystallized anhydrous sodium chlorite at such higher temperature.

5. A process for the separation of sodium chlorite and potassium chlorate from solutions containing these salts which comprises progressively evaporating the solution at a temperature above 34 C. to crystallize potassium chlorate until solution approximates the eutectic composition having a saturation temperature of about 34 C., separating the potassium chlorate thus crystallized, and thereafter cooling the remaining solution in the absence of solid NaClOz3I-I2O to about 25 C. and separating therefrom at said lower temperature an additional amount of crystallized potassium chlorate, thereafter seeding the remaining solution with NaClOz-3H2O crystals to crystallize NaClOz-3H2O, separating the thus crystallized NaClO2-3H2O from the mother liquor, and recycling the mother liquor to the initial evaporation step.

6. A process for the separation of sodium chlorite and potassium chlorat from solutions containing these salts which comprises progressively evaporating the solution at a temperature above 34 C. to crystallize potassium chlorate until solution approximates the eutectic composition having a saturation temperature of about 34 C., separating the potassium chlorate thus crystallized, and thereafter cooling the remaining solution in the absence of solid NaClOz-3I-I2O to about 25 C. and separating therefrom at said lower temperature an additional amount of crystallized potassium chlorate, thereafter seeding the remaining solution with NaClO2-3H2O crystals to crystallize NaClO2-3HzO, separating the thus crystallized NaClOz-3H2O from the mother liquor, heating the crystallized REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,031,681 Vincent Feb. 25, 1936 2,046,830 Logan July 7, 1936 2,169,066 Cunningham Aug. 3, 1939 OTHER REFERENCES Seidell: Solubilities of Inorg. and Org. Compounds, vol. I, D. Van Nostrand Co, New York, 1919, pp. 513 and 639.

Mellor: Treatise on Inorganic and Theoretical Chemistry, vol. 2, Longmans, Green & Co., New York city, 1922, pp. 282 and 283. 

1. A PROCESS FOR THE SEPARATION OF SODIUM CHLORITE AND POTASSIUM CHLORATE FROM SOLUTIONS CONTAINING THESE SALTS WHICH COMPRISES PROGRESSIVELY EVAPORATING THE SOLUTION AT TEMPERATURES ABOVE 34*C. SO AS TO CRYSTALLIZE POTASSIUM CHLORATE UNTIL THE SOLUTION REACHES THE EUTECTIC COMPOSITION HAVING A SATURATION TEMPERATURE OF ABOUT 34*C., SEPARATING THE THUS CRYSTALLIZED POTASSIUM CHLORATE, THEREAFTER COOLING THE REMAINING SOLUTION BELOW 34*C. TO CRYSTALLIZE A MIXTURE OF POTASSIUM CHLORATE AND NACLO2$3H2O, SEPARATING THE MIXTURE FROM THE MOTHER LIQUOR, HEATING THE MIXTURE ABOVE THE TRANSITION POINT OF NACLO2$EH2O TO DISSOLVE THE POTASSIUM CHLORATE AND TO FORM A SLURRY OF SOLID ANHYDROUS SODIUM CHLORITE IN A SATURATED SOLUTION THEREOF, AND SEPARATING THE SOLID SODIUM CHLORITE FROM THE HEATED SOLUTION. 